What Role Did Accused Soldier's Brain Injury Play in Afghan Massacre? (UPDATED)

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What Role Did Accused Soldier's Brain Injury Play in Afghan Massacre? (UPDATED)

It's incredibly difficult to surmise what might have pushed one American sergeant to allegedly massacre 16 Afghan civilians. But new details about the still-unnamed staff sergeant's background suggest that brain damage, wrought by a traumatic brain injury during an earlier deployment, might have been a contributing factor.

It would be misleading, and downright reductionist, to suggest that TBI sufferers will commit murders. But scientists have linked brain trauma to some violent episodes.

In an interview with ABC News on Monday, an unnamed source claimed that the sergeant suffered a TBI sometime in a past deployment, either by "hitting his head on the hatch of a vehicle or in a car accident." A subsequent story from Reuters reported that the TBI occurred as recently as 2010. The alleged shooter is said to have later undergone TBI-specific treatment at Joint Base Lewis-McChord, before being cleared for duty and then redeployed. He also reportedly passed typical behavioral health assessments during his enlistment.

The sergeant is hardly alone in suffering from a brain injury while overseas. TBIs, along with post-traumatic stress disorder, are widely renowned as "the signature wounds" of the wars in Iraq and Afghanistan. An estimated 200,000 soldiers have been diagnosed with a TBI since the wars started. That estimate is most likely a low-ball. And clearly the vast, vast, vast majority of those TBI sufferers have not turned homicidal.

The specifics of a link between TBI and subsequent violent behavior haven't been entirely parsed out by scientists. And surely no one factor could possibly lead to the kind of rampage seen in Afghanistan on Sunday. But myriad studies have concluded that a connection between TBI and violence does seem to exist.

One report followed 850 young civilian adults over eight years, and found that those who'd suffered a TBI "reported more interpersonal violence" than their peers. Another, out of Sweden, tracked over 20,000 people for 35 years. That one, published earlier this year, noted that 9 percent of all TBI-afflicted study participants were implicated in a violent crime at some point after sustaining the injury. By comparison, only 3 percent of those without a brain injury ever committed a violent crime. The researchers concluded that TBI "significantly increased [the] risk" that an individual would behave violently.

A major 2009 study of Iraq war veterans suffering from TBIs published in the New England Journal of Medicine found that TBI sufferers experienced "significantly more" mental health problems in the years following their injury. In particular, the patients exhibited symptoms of PTSD, which can include depression and aggression, though the study doesn't specify which PTSD symptoms were most severely exacerbated.

One older military study even suggests a connection that scientists are only now starting to unravel: the possibility that physical brain damage from a TBI actually "primes" the brain for PTSD. In 1996, a team writing in the journal Neurologist reported the findings of their study on 279 Vietnam-era veterans who'd suffered TBIs with varying degrees of severity during their deployment. That team found a strong link between TBIs and aggression, but noted that the presence of aggressive behavior seemed more strongly linked to the location of the brain damage, rather than how severe it was. In particular, veterans with damage to the brain's frontal lobe were more likely to exhibit violent behaviors.

The frontal lobe is a realm quite familiar to scientists studying both TBI and PTSD. It's the part of the brain responsible for higher functions, including impulse control, understanding right from wrong and anticipating the consequences of one's actions. So it's hardly surprising that the frontal lobe has been, time and time again, linked to PTSD, whose sufferers are much more likely to exhibit aggression and violence than their unaffected peers. It's also a brain region particularly vulnerable to the head-rattling damage of a concussive injury.

Regardless of that potential connection, TBI still seems implicated in violent behavior on its own – regardless of a PTSD diagnosis. One 2003 study, for example, compared patients who'd suffered a TBI with those who'd experienced "multiple traumas" but no brain damage. Nearly 40 percent of TBI sufferers exhibited violent behavior, compared to a mere 11 percent of those without a brain injury.

Of course, it's important to note that there's no indication the soldier implicated in yesterday's massacre had been diagnosed with PTSD. But the Pentagon brass and psychiatric experts have long acknowledged that one's risk for developing the syndrome increases with repeat deployments. Research by the Army itself has already warned that a second deployment increases rates of acute combat stress – which is a significant precursor to long-term PTSD – characterized by anxiety attacks and disorientation, among other symptoms, by 50 percent. The alleged shooter was on his fourth combat deployment.

Surely, the myth of the loco, time-bomb-ticking vet is a stereotype that needs to be rejected once and for all. But the role that TBI plays in spurring violent behavior remains an open question. And determining why the awful violence in Panjwei happened at all, and whether brain damage or PTSD (or both) had anything to do with that or other frightening episodes of soldier violence, might take years for scientists to unravel.

And while they do, it's likely that the military's mental health resources – already widely criticized, far from fail-proof and bursting at the seams – will be called on to do even better by today's troops.

UPDATED: Joint Base Lewis-McChord, where the accused soldier was treated for TBI before being deployed to Afghanistan, has recently been implicated in an investigation over misdiagnosed PTSD cases. Again, officials haven't stated whether soldier in particular had been diagnosed with PTSD at any point during enlistment. But as reported in the Washington Post today, Army investigators are currently poring over thousands of cases to see whether soldiers with PTSD at Lewis-McChord were diagnosed with a lesser ailment (like personality disorder). Already, the medical diagnoses of 285 soldiers will be re-evaluated by doctors.